Engines which run on fuels such as gasoline or diesel fuel typically include a tank which stores the fuel that has not yet been utilized by the engine. These fuel tanks include openings through which a user can refuel when the level of fuel within the tank decreases. When not opened for refueling, the opening is covered by a fuel cap which seals the fuel tank. When the fuel cap is secured to the tank, the fuel tank may be vented. Proper venting of fuel tanks in cars or vehicles is important to reduce emissions of hydrocarbon fuels into the atmosphere and thus to reduce pollution of the atmosphere.